The first production guns had the skinny triggers in combination with the aluminum alloy grip frames.
When they went to steel grip frames the triggers went wide.
As mentioned by Contender the Brass Grip Frames used the Wide Super Blackhawk Trigger (Grooved), probably safe to assume it was the "Part" they had in the parts bin / for the OM Super Blackhawk.
Then as the Old Model Super Blackhawk got changed to a New Model,,,
The Old Model Super Blackhawk Triggers, in the parts bin, were used up in the Old Army's.
This is when I assume Ruger only needed to make a Old Model Trigger, for the Old Army ONLY, and that's when the new production Wide Old Model Old Army Trigger went SMOOTH. My observations have been these triggers show up in later production guns with the "WARNING" on the barrel. (~1977?)
As for Stainless, I have only had 3, SN# 646, 145-0242x, 0480X all early production guns, All have grooved wide triggers, and no "Warning" on the barrel.
I also think that any "STEEL" grip frame Ruger has ever made has ONLY a WIDE trigger slot. My thinking here is Casting, Milling, Manufacture Process?...
My assumptions are my observations, I welcome other's knowledge, thoughts, assumptions or ideas.... :wink: